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.FUEL. ' 169
The reaction: C+H20=CO+H2 is endothermic; i. e., it takes place with expenditure of heat. The splitting up of H20 requires 57.6 heat units, of which only 28.6 are supplied by the reaction C-|-0=CO, so that 29 heat units has to be made good. These 28 heat units must be supplied apart from the incandescent fuel, the temperature of which soon falls below the point where the reaction C4-H20=CO+H2 is prevailing (assumed to be above 1000° C.)-Below this temperature another reaction comes into play, viz., Gl+2H20==CO,-f-2H2, which produces a gas composed of one-third inert carbon dioxide and two-thirds combustible hydrogen. This second reaction is also of endothermic character, and if real water gas is to be made, the operation is divided into two distinct phases or stages. Beginning with incandescent coal in a generator 2 or 3 m. in height, at a temperature of about 1200° C., steam, preferably in the superheated state, is introduced and water gas is formed according to the reaction,
Soon, however, the temperature sinks and carbon dioxide C02 is produced by the secondary reaction,
Before the carbon dioxide begins to prevail, the steam must be shut off, the temperature being then below 1000° C. This whole period of steaming lasts four or five minutes, and the gas contains by volume 48 to 50% H, 40 to 45fo CO, 4 to 5% C02 and 4 or 5% N, and has a value of about 2600 heat units per cu. m. After the steam is shut off, the blowing up begins; air is blown into the generator. When the temperature reaches the required degree the air is shut off and the generator is ready for another steaming. Until recently the blowing up was carried on as in the making of ordinary producer gas, but in the Dellwik-Fleischer process* such conditions are established in the generator that complete combustion to carbon dioxide is obtained. The difference in results are outlined herewith:
* JournaZ I. and S. I., May, 1900.